Many electronic devices incorporate thin displays, often referred to as "flat-panel" displays, for displaying alphanumeric information or other types of indicia. The most common type of flat panel display is the liquid crystal display. A typical liquid crystal display device comprises a cell containing a volume liquid crystal material separated by a first and second transparent electrodes. Overlying the first and second electrodes are first and second polarizers, respectively. In response to an electric field, the liquid crystal material in the cell twists (rotates) the plane of polarization of the light passing therethrough. If the polarizers are crossed so that their planes or polarization are orthogonal to each other, then light will pass through the display when the electrodes are energized. Conversely, when the first and second polarizers are aligned, no light will pass through the cell. Generally, there are two types of liquid crystal displays. The first type of display, known as the "reflective-type", is characterized by mirror placed behind the second polarizer for reflecting the light exiting the second polarizer back into the cell. The other type of display, known as the "transmissive type", is characterized by a light source positioned behind the second polarizer for transmitting light through the cell when the cell is energized.
Liquid crystal displays can be made to display various indicia, including alphanumeric characters, by patterning one or both of the electrodes. As may be appreciated, the pattern of the electric field applied to the liquid crystal material is dependent on the spatial nature of the electrodes. With present day transmissive-type liquid crystal displays, the first electrode, (i.e., the one furthest from the light source) is usually uniform. In contrast, the second electrode (i.e., the one closest to the light source) is patterned into a plurality of discrete elements. Each discrete element corresponds to an individual portion (pixel) of the image produced by the liquid crystal display. By applying an electric field between the first electrode and an element of the second electrode, the energized element of the second electrode will pass light from the light source. As a result, the corresponding pixel in the image displayed by the liquid crystal display device appears bright. In the case of a color display, red, green and blue filters may be placed proximate to different elements of the second electrode to alter the color of the image displayed by the liquid crystal display.
Liquid crystal displays of the type described are each fabricated by forming a pair of flat panel display plates. Each flat panel display plate includes an electrode on a light transmissive electrode support, (e.g., a thin layer of plastic or glass). The electrode and its accompanying support may be adhered to a polarizer in the event that the support itself lacks the capability of polarizing light. Once a pair of flat panel display plates is formed, then a volume of liquid crystal material is placed between the plates to yield a liquid crystal display device.
During the fabrication process, it is desirable to test each flat panel display plate prior to final assembly. Present-day test techniques for non-invasively testing flat panel display plates are slow and thus limit plate throughput. Invasive techniques, while useful, are only suitable for sample lots, not for continuous testing.
Thus, them is a need for an easy-to-use, non-invasive technique for rapidly testing a flat-panel display plate.